linux-kernel - Re: [PATCH] block: fix RO partition with RW disk

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Message-ID: <2f424a79-059b-be41-8f60-1397e2f9fdcf@oracle.com>
Date:   Mon, 5 Aug 2019 19:31:10 -0700
From:   Junxiao Bi <junxiao.bi@...cle.com>
To:     Dongli Zhang <dongli.zhang@...cle.com>
Cc:     linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
        axboe@...nel.dk, martin.petersen@...cle.com,
        "osandov@...com" <osandov@...com>
Subject: Re: [PATCH] block: fix RO partition with RW disk

Hi Dongli,

I think it's possible. A rough test case i can think is to create one 
loop device, one process issued BLKRRPART ioctl to re-read partition 
table(this will drop all partitions and recreate again) and another 
process set disk ro then rw. Let them race and check whether ro 
partition was left.

Thanks,

Junxiao.

On 8/5/19 6:22 PM, Dongli Zhang wrote:
> Hi Junxiao,
>
> While this is reported by md, is it possible to reproduce the error on purpose
> with other device (e.g., loop) and add a test to blktests?
>
> Dongli Zhang
>
> On 8/6/19 4:01 AM, Junxiao Bi wrote:
>> When md raid1 was used with imsm metadata, during the boot stage,
>> the raid device will first be set to readonly, then mdmon will set
>> it read-write later. When there were some partitions in this device,
>> the following race would make some partition left ro and fail to mount.
>>
>> CPU 1:                                                 CPU 2:
>> add_partition()                                        set_disk_ro() //set disk RW
>>   //disk was RO, so partition set to RO
>>   p->policy = get_disk_ro(disk);
>>                                                          if (disk->part0.policy != flag) {
>>                                                              set_disk_ro_uevent(disk, flag);
>>                                                              // disk set to RW
>>                                                              disk->part0.policy = flag;
>>                                                          }
>>                                                          // set all exit partition to RW
>>                                                          while ((part = disk_part_iter_next(&piter)))
>>                                                              part->policy = flag;
>>   // this part was not yet added, so it was still RO
>>   rcu_assign_pointer(ptbl->part[partno], p);
>>
>> Move RO status setting of partitions after they were added into partition
>> table and introduce a mutex to sync RO status between disk and partitions.
>>
>> Signed-off-by: Junxiao Bi <junxiao.bi@...cle.com>
>> ---
>>   block/genhd.c             | 3 +++
>>   block/partition-generic.c | 5 ++++-
>>   include/linux/genhd.h     | 1 +
>>   3 files changed, 8 insertions(+), 1 deletion(-)
>>
>> diff --git a/block/genhd.c b/block/genhd.c
>> index 54f1f0d381f4..f3cce1d354cf 100644
>> --- a/block/genhd.c
>> +++ b/block/genhd.c
>> @@ -1479,6 +1479,7 @@ struct gendisk *__alloc_disk_node(int minors, int node_id)
>>   		}
>>   		ptbl = rcu_dereference_protected(disk->part_tbl, 1);
>>   		rcu_assign_pointer(ptbl->part[0], &disk->part0);
>> +		mutex_init(&disk->part_lock);
>>   
>>   		/*
>>   		 * set_capacity() and get_capacity() currently don't use
>> @@ -1570,6 +1571,7 @@ void set_disk_ro(struct gendisk *disk, int flag)
>>   	struct disk_part_iter piter;
>>   	struct hd_struct *part;
>>   
>> +	mutex_lock(&disk->part_lock);
>>   	if (disk->part0.policy != flag) {
>>   		set_disk_ro_uevent(disk, flag);
>>   		disk->part0.policy = flag;
>> @@ -1579,6 +1581,7 @@ void set_disk_ro(struct gendisk *disk, int flag)
>>   	while ((part = disk_part_iter_next(&piter)))
>>   		part->policy = flag;
>>   	disk_part_iter_exit(&piter);
>> +	mutex_unlock(&disk->part_lock);
>>   }
>>   
>>   EXPORT_SYMBOL(set_disk_ro);
>> diff --git a/block/partition-generic.c b/block/partition-generic.c
>> index aee643ce13d1..63cb6fb996ff 100644
>> --- a/block/partition-generic.c
>> +++ b/block/partition-generic.c
>> @@ -345,7 +345,6 @@ struct hd_struct *add_partition(struct gendisk *disk, int partno,
>>   		queue_limit_discard_alignment(&disk->queue->limits, start);
>>   	p->nr_sects = len;
>>   	p->partno = partno;
>> -	p->policy = get_disk_ro(disk);
>>   
>>   	if (info) {
>>   		struct partition_meta_info *pinfo = alloc_part_info(disk);
>> @@ -401,6 +400,10 @@ struct hd_struct *add_partition(struct gendisk *disk, int partno,
>>   	/* everything is up and running, commence */
>>   	rcu_assign_pointer(ptbl->part[partno], p);
>>   
>> +	mutex_lock(&disk->part_lock);
>> +	p->policy = get_disk_ro(disk);
>> +	mutex_unlock(&disk->part_lock);
>> +
>>   	/* suppress uevent if the disk suppresses it */
>>   	if (!dev_get_uevent_suppress(ddev))
>>   		kobject_uevent(&pdev->kobj, KOBJ_ADD);
>> diff --git a/include/linux/genhd.h b/include/linux/genhd.h
>> index 8b5330dd5ac0..df6ddca8a92c 100644
>> --- a/include/linux/genhd.h
>> +++ b/include/linux/genhd.h
>> @@ -201,6 +201,7 @@ struct gendisk {
>>   	 */
>>   	struct disk_part_tbl __rcu *part_tbl;
>>   	struct hd_struct part0;
>> +	struct mutex part_lock;
>>   
>>   	const struct block_device_operations *fops;
>>   	struct request_queue *queue;
>>